The disclosure relates generally to combined cycle power plant system, and more particularly, to components and systems for reducing thermal stress experienced by manifolds within a heat recovery steam generator (HRSG) of the combined cycle power plant system.
Power systems typically include a variety of different turbomachines and/or systems that are used to generate operational load and/or power output. Two conventional power systems used to generate operational loads include gas turbine systems and combined cycle power plants, which typically include a gas turbine system(s). Conventional combined cycle power plants employ one or multiple gas turbine system(s) operatively coupled to one or multiple steam turbine system(s). The gas turbine system includes a compressor coupled to a gas turbine. The gas turbine is usually coupled to and drives an external component, such as a generator, for producing a load or power output. The steam turbine system includes a high pressure (HP) turbine portion operatively coupled to an intermediate pressure (IP) turbine portion that, in turn, is coupled to a low pressure (LP) turbine. Similar to the gas turbine of the gas turbine system, the HP, IP and LP turbines are employed to drive an external component (e.g., generator). In a typical combined cycle power plant, exhaust gas from the gas turbine is passed to a heat recovery steam generator (HRSG), which may be used to reheat and provide steam to the various turbines of the steam turbine system for enhanced efficiency of the system and/or power plant. Downstream of the HRSG the exhaust gas is released to the atmosphere through a stack.
However, during operation of the power system, portions and/or components may experience high stress due to rapid temperature change of the components, which results in undesirable thermal fatigue of the components. For example, when the power system is first started during a start-up procedure, the HRSG may immediately begin to generate high temperature steam. This high temperature steam may be provided, supplied and/or move through portions of a boiler module of the HRSG which may be at reduced or pre-start temperature (e.g., ambient temperature) that is significantly lower than the temperature of the high temperature steam. As a result of the exposure to the high temperature steam the portions of the boiler module of the HRSG may undergo a rapid temperature change. The rapid temperature change may increase the stress experienced by the boiler module and/or its various components exposed to the high temperature steam during the start-up procedure. Once the power system is operational for a predetermined amount of time, the components of the boiler module may be consistently heated to an operational temperature, which in turn may reduce the stress experienced by the components. The reduction of the stress through the repetition of the event across the operational life may reduce the thermal fatigue experienced by the components.
However, when the power plant is shut down again (e.g., not operational), the temperature of the components forming the boiler module may again decrease to the pre-start temperature, and upon the next start-up procedure, may experience the same high stress. Because of continued exposure to high stress, components of the boiler module may degrade and/or become damaged due to thermal fatigue, which may result in reduced operational performance/reliability and/or failure of the power system. Additionally, because the components become damaged, they eventually need to be replaced, which requires the power system to be completely shutdown or inoperable while the damaged components are replaced. The necessity to replace the damaged parts within the power system may reduce the operational time of the power system, which reduces the overall power or load output, and also increases the maintenance costs (e.g., component replacement) for the power system over the operational life of the system.